The invention relates to a method for sequentially recording interferometric deep sectional images. The invention further relates to a device for carrying out the method.
The recording of interferometric deep sectional images is associated with the problem that the device only allows a limited measuring depth for a particular reference arm length. In Fourier domain systems, the measuring depth is limited by the resolution of the spectral apparatus. Rapidly operating systems typically detect depths with a distance of up to 10 mm from the reference plane with acceptable signal-to-noise ratio.
In addition, the depth of field of the optical system that is employed often limits the measuring depths when recording interferometric deep sectional images. Typically, only ranges in the order of magnitude of the Rayleigh length can be recorded with good lateral resolution and acceptable signal-to-noise ratio. An expansion of the measuring depth to several times the Rayleigh length often requires the focal position to be adjusted.
One of the factors that the depth resolution of interferometric deep sectional images depends on is the adaptation of the dispersion in the arms of the interferometer that is employed. The dispersion of conventional systems is only adapted to one measuring depth, so that expanding the measuring depth generally entails a loss of axial resolution.
According to the invention, these problems listed here are to be solved for rapidly operating interferometric imaging systems.
So as to adjust the region of a sample that is scanned with a good signal-to-noise ratio to a new depth, the path length difference between the sample path and the reference path, and optionally the imaging geometry and the focus position, as well as the dispersion, must be changed. In particular in the case of movable samples (for example when measuring the eye), the change of the path length difference and, if required, the change of the focus position, and optionally the change of the dispersion adaptation, must take place quickly, so as to obtain information about the relative positions of the scanned regions with respect to each other, and optionally be able to assemble a complete deep sectional image from several sequentially recorded individual deep sectional images. Modern interferometric measuring systems achieve frame rates of several 100 Hz. A controlled change of the position of the measuring apparatus relative to the sample or the position of the mirror in the reference arm is not possible when switching to differing regions within a time of considerably less than 10 ms (for example 1 ms for a maximum of 10% dead time at a frame rate of 100 Hz), because here paths of several mm must be covered.